<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    div {
      background-color: brown;
      width: 200px;
      height: 100px;

      /* 边框盒子模型包括：内容+内边距+边框 */
      box-sizing: border-box;
      /* 内边距 */
      padding: 20px;
      /* 边框 */
      border: 10px solid red;
      /* 外边距 */
      margin: 20px;
    }
  </style>
</head>
<body>
  <div>内容</div>
  <div>内容</div>
</body>
</html>